Agathoxylon holbavicum, Iamandei & Iamandei & Grădinaru, 2018

Iamandei, Stănilă, Iamandei, Eugenia & Grădinaru, Eugen, 2018, Contributions To The Study Of The Early Jurassic Petrified Forest Of Holbav And Cristian Areas (Brașov Region, South Carpathians, Romania). 1 Part, Acta Palaeontologica Romaniae 14 (2), pp. 3-34 : 9-12

Agathoxylon holbavicum sp. nov.

Fig. 4 a-i.

The studied material

The studied material is represented by a decimetric-sized piece of silicified wood collected from Holbav locality area (BraȘov County), on Maiului brook, in Lower Jurassic continental pyroclastic deposits considered of Pliensbachian age. The studied sample is a trunk or thick-branch fragment with decimetric size, dark to black color and by magnifying glass, or even by naked eye, a regular fibrous structure, suggesting a conifer wood. The studied specimen with the field-number 1041 belong to "Grădinaru Collection", and is deposited in the collections of the Geological Institute of Romania ( G. I. R. Collections), hosted by the National Geological Museum, Bucharest, under the inventory number 27611.

Microscopic description

The studied specimen presents s e c o n d a r y w o o d with tracheidoxylic structure, with relatively distinct growth-rings boundaries and devoid of any normal or traumatic resin canals.

T r a c h e i d s - with polygonal cross-section with slightly rounded corners, often determining small intercellular spaces. With polygonal rounded lumina unequally sized with radial/tangential diameters of 20-30/20-38 μm and thick walls, of 8-13 μm (double wall), thinner in early-wood: 5-8 μm the double- wall. There are 1-9 radial regular rows of tracheids between two successive rays and the density is (675)1155-1650 tracheids per mm2. Tangentially seen, the tracheids are unpitted. The radial pitting is typical araucarian, as uniseriate vertical rows of contiguous hexagonal pits and as biseriate rows with alternate contiguous also hexagonal bordered pits with a diameter of 17-20 μm, and oblique elliptic to vertical apertures of 7.5/2.3 μm in diameters. There are no crassulae or helical thickenings.

A x i a l p a r e n c h y m a - is absent.

M e d u l l a r y r a y s - are thin, rectilinear and are constituted of quadrangular cells with smooth horizontal walls. Tangentially the rays have 1-19 cells in height, i.e. 20-380 μm high. Sometimes the taller rays are locally biseriate, so often they appear as biseriate rays with long endings. The ray cells are polygonal slightly rounded and flattened, unequal in size and relatively thick walled: of 2.5-3.1 μm the simple wall. The ray density is 8-14 rays per horizontal tangential millimeter. Radially the rays are homocellular, cells all procumbent of 20-30 μm high, moderately thick-walled: 5-6.2 μm the double wall. Indentures were not observed. Within the marginal rows the ray-cells are higher, of 30-40(-45) μm, with their outer wall slightly wavy. The typical araucarioid cross-fields have 1-6(-9) oculipores, cupressoid (tending to araucarioid) pits, slightly rounded or hexagonal, of 9-13 μm in diameter, with round or short elliptic tilted apertures to vertical, of 3.5-5.5 μm. In the cross- fields with body ray-cells the pits are 1-3 arranged in one horizontal row, or 2- 6 pits on 2 rows, alternately arranged, or slightly irregular. In the marginal fields they are more numerous, alternately arranged, or slightly irregular, in 2-3 horizontal superposed rows. Often, isolated ray-cells or rows of ray-cells in the body or even marginal cells are full of resin content, visible also in tangential view.

Affinities and discussions

The studied specimen presents a combination of xylotomic characters similar to the extant araucariaceous conifers, consequently a comparison with this type of wood structure was performed and we observed similitude with Araucaria and Agathis (see Greguss, 1955).

Many fossil woods with tracheidoxylic structure collected from the Palaeozoic and Mesozoic formations have been recorded as species of Araucarioxylon and Dadoxylon , genera whose status is not legitimate in all cases and thus they have been invalidated (see Philippe, 1993, 1995; Philippe & Barbacka, 1997; Rössler et al., 2014). Thus, for this type of wood was kept the genus Agathoxylon Hartig , validly described and published and not yet typified, even if the type material is probably lost (Philippe, 1993).

Other genera as Dammaroxylon Schultze-Motel and Pseudagathoxylon Greguss are considered as taxonomic synonym of Agathoxylon , respectively of Simplicioxylon Andreanszky which is a valid genus (see Philippe & Bamford, 2008).

Using the identification key proposed by Philippe (1993) and Philippe & Bamford (2008) for tracheidoxyls with araucarioid cross-fields, we found that the here studied specimen fits to Agathoxylon Hartig. The generotype, A. cordaianum Hartig , presents similar features having araucarian radial pitting, araucarioid cross-fields and sometimes axial parenchyma. Although the original diagnosis of the genus Agathoxylon Hartig (Hartig, 1848; Philippe & Bamford, 2008) includes the presence of axial parenchyma as a diagnostic character (a feature absent in several specimens referred to Agathoxylon ), Philippe (1995) reformulated the original diagnosis proposed by Hartig (1848), allowing the inclusion of woods with and without axial parenchyma.

This taxonomic decision is adequate since a high number of genera have already been proposed, and erecting another one for including Agathoxylon -like woods without axial parenchyma would lead to a more confuse taxonomy.

- We take into account that many European Cretaceous species of Araucarioxylon, Dadoxylon (Araucarioxylon) , or Dadoxylon (see Schultze-Motel, 1962, 1966), only some of them equivalent to Agathoxylon , it is difficult to compare our material with them, but since a serious revision of them is missing. Also, in some recent partial revisions of the Cretaceous woods from Hungary, Italy, France and Austria, it is shown that many of them come from the Lower Cretaceous, or are not tracheidoxyls (Philippe, 1995; Philippe & Barbacka, 1997).

- Some Cretaceous similar tracheidoxyls come also from the Carpathian area (Apuseni mts.): Agathoxylon sp. (described initially as Araucarioxylon sp.) of Petrescu & Nuţu (1971), Agathoxylon ultimum and A. formosum , the last described as species of Dammaroxylon (by Iamandei & Iamandei, 2004), all of them presenting the typical araucarian combination of xylotomic characters.

Numerous other Jurassic–Early Cretaceous fossil-woods from Mid-Eastern Europe described as Agathoxylon (or equivalents that were reattributed to Agathoxylon ) are cited by Philippe et al. (2006) as folows:

- Agathoxylon agathiforme (Kedves) Philippe et Barbacka , (in Philippe & Barbacka, 1997) and A. parenchymatosum (Greguss) Philippe, Zijlstra et Barbacka (in Philippe et al., 1999), both of them from the upper Liassic of Hungary.

- Agathoxylon desnoyersii (Lemoigne) Philippe, 1995 from the middle Callovian of Poland, initially described as Araucarioxylon sp. by Reymanówna (1956), redescribed by Lemoigne as a species of Brachyphyllum and now considered only as a junior taxonomical syonym (Philippe et al., 2018).

- Agathoxylon pannonicum (Greguss) Barale, Barbacka et Philippe , from the Aptian or Albian of Hungary (see Greguss, 1952; Barale et al., 2002).

Numerous specimens having the typical xylotomical characters: araucarian radial pitting on biseriate rows, contiguous pits, rarely spaced, and only occasionally as uniseriate rows. The cross-field pits are araucarioid, usually as 1-2 cupressoid oculipores arranged in araucarioid manner in the cross-fields were described as Agathoxylon sp. either as new data or reattributed to Agathoxylon , come from a large area:

- From the Bajocian and Barremian of Bulgaria (Philippe et al., 2006);

- From the Liassic of Hungary (Philippe & Barbacka, 1997; Philippe et al., 1999);

- From the Rhaeto–Liassic and from the Bathonian of Poland (in Philippe et al., 2006);

- From the Bathonian of Romania (Philippe et al., 1999), - From the late Cretaceous of Spain (García Esteban et al., 2006);

- From Upper Cretaceous (upper Maastrichtian), Dutlu Formation of Turkey (Kutluk et al., 2012);

- Mencl et al. (2013) discuss in their paper the occurrence, the anatomical features and the taxonomy of numerous silicified woods from the Late Paleozoic Basins of the Czech Republic attributed to Agathoxylon .

- Philippe et al. (2015) reattributed an old taxon of Unger described as Pinites from the Keuper sandstones in Attelsdorf, Germany as Agathoxylon keuperianum nov. comb.

- Also Philippe et al. (2018) studying an old collection of Cretaceus fossil woods from France ("Lignier collection"), reattributed some badly identified woods also to Agathoxylon as new species or new combinations ( A. crasseradiatum , A. tranchantii , or simply to Agathoxylon sp. ).

It is obvious that this type of coniferous genus was widespread on the Earth since it was described from already all the continents. Thus, many species were described from the Middle to Upper Cretaceous of Far-East Asia and we quote: A. tankoense Stopes & Fujii (initially described as Dadoxylon tankoense (Stopes et Fujii) Shimakura (in Philippe, 1993), then an Agathoxylon kiiense (Ogura) Oh et al. , A. togeumense Oh et al. , A. byeongpungense (Kim et al.) Oh et al. , (in Schultze-Motel,

1966 and in Oh et al., 2011). - From Africa, we cite a species ( Agathoxylon lifiyii ) described from the Upper Cretaceous of Egypt (Karga Oasis) by Youssef et al. (2000) having typical generic features, and also two Permo-Triassic species ( A. africanum , A. karooensis ) described by Bamford (2016), in which the araucarian radial pitting is preserved as "Steinkerne" that mimic the mixed type of pitting (see Bamford, 2016), details not observed in our specimen.

- From South America, from the Middle Jurassic of Argentina an Agathoxylon matildense with distinct growth-rings, uniseriate pitting on the radial tracheidal walls with contiguous round pits and cross-fields with 4-5 cupressoid pits irregularly arranged and very low rays was described by Zamuner & Falaschi (2005) and other quasisimilar four species by Kloster & Gnaedinger (2017), all of them different of our specimen.

- Also from the Aptian of Patagonia, Vera & Césari (2012) described an Agathoxylon , a wood characterized by araucarian tracheid pitting, predominantly uniseriate, rarely biseriate arranged, alternate to opposite and by araucarioid cross-field pits, typical for Araucariaceae . It is true that this type of wood appears also to the Pteridospermales and Cheirolepidiaceae , and the older Agathoxylon could represent stems of various cordaitalean - conifer origin (Philippe et al., 2004a). In this respect must be remind that in our specimen description was observed that the taller rays are locally biseriate, often with aspect of biseriate rays with long endings, and also that often ray cells are full of resin content.

- From the Paleocene and Eocene of Western Antarctica some Agathoxylon species were described suggesting even possible austral Araucariaceae-dominated forests ( Pujana et al., 2014; 2015; Mirabelli et al. 2018).

After this discussion of the widespread spread of this Mesozoic genus and taking into account the opinion of García Esteban et al. (2006) on the difficulty of distinguishing species of this genus which is species plethoric and the distinction of species is very difficult, so they preferred to describe their material only at generic level, we still believe that we are faced with a new species of Agathoxylon that lived within Carpathian area at least during Early Jurassic.

Thus, the studied specimen is characterized by typical araucarian pitting in uniseriate and biseriate-alternate arrangement of contiguous hexagonal pits with oblique-elliptic apertures and typical araucarioid cross-fields with numerous polygonal pits alternately arranged on 1-3 superposed horizontal rows. We named this new species Agathoxylon holbavicum sp. nov., remembering the name of the original area (Holbav) from where the studied material was collected. The specimen with inventory no. 27611 (field number 1041) was designated as holotype hosted now in G. I. R. Collections, in the National Geological Museum , Bucharest .

Diagnosis of the new species Agathoxylon holbavicum sp. nov.:

Tracheidoxyl with typical araucarian cross-section, with distinct growth rings, without resin canals or axial parenchyma. Tangential tracheidal walls unpitted, radial pitting typical araucarian, uniseriate and biseriate alternate, with contiguous, hexagonal pits with oblique elliptic to vertical apertures. Rays - uniseriate, locally biseriate, homocellular, marginals higher, with outer wall slightly waved, often with resin content. Cross-fields typical araucarioid with 1-9 oculipores as araucarioid pits alternately arranged on 1-3 horizontal rows, hexagonal or slightly rounded, with short elliptic tilted apertures to vertical.

Figures

Fig. 4 Agathoxylon holbavicum sp. nov. - holotype - inventory no. 27611 (field no. 1041). a-c Cross section - tracheids polygonal with rounded corners, and linear rays. d-f Tangential section - uniseriate rays with biseriate storeys with polygonal ray-cells, with lateral empty spaces; unpitted tracheids. g-i Radial section - araucarian radial piting on tracheids, alternate hexagonal pits, araucarioid cross-fields with 2-3 superposed rows of hexagonal pits.